Fluorophosphate glass and process of making same

ABSTRACT

A fluorophosphate glass which has an index of refraction ne of more than 1.57, an Abbe number  nu e of less than 70, and a relatively high positive anomalous partial dispersion + DELTA  nu e is provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process of producing a fluorophosphate glass and more particularly to a process of producing a fluorophosphate glass having an index of refraction n_(e) of more than 1.57 and an Abbe number ν_(e) of less than 70, said glass having furthermore a relatively high positive anomalous partial dispersion +Δν_(e), and to such a glass.

2. Description of the Prior Art

It is known to produce, by melting, glasses being based on metaphosphates of Group II and Group III of the periodic system with the addition of simple and/or complex inorganic fluorides, said glasses having a positive anomalous partial dispersion.

Thus there is known from U.S. Pat. No. 3,492,136 a process for the manufacture of a fluorophosphate glass the starting mixture of which, in addition to calcium and/or aluminum metaphosphate, also contains alkaline earth metal fluorides and one of the compounds potassium meta-arsenate, potassium heptafluoro tantalate, or, respectively, potassium hexafluoro titanate. The glass produced by this known process have indices of refraction n_(e) between 1.53 and 1.55. Such indices must be considered relatively high for this type of glass. Furthermore, U.S. Pat. No. 3,671,276 discloses an improvement in the process described in U.S. Pat. No. 3,492,136 by which fluorophosphate glasses having indices of refraction n_(e) between 1.50 and 1.56 can be produced.

Thus according to these known processes it was possible to produce optical fluorophosphate glasses of medium to low dispersion -- corresponding to a medium to high Abbe number ν_(e) -- and of indices of refraction n_(e) between 1.53 and 1.56. Such glasses, furthermore, exhibit a positive anomalous partial dispersion +Δν_(e).

It is, however, of interest with respect to certain fields of use in the optical industry to provide glasses of even higher refractive values n_(e) >1.57 and of optimum dispersion, but which meet the requirements of the calculating optician, namely requiring that such glasses also retain, or at least only slightly reduce, their positive anomalous partial dispersion values. Such glasses, heretofore, have not been produced.

SUMMARY OF THE INVENTION

It is one object of the present invention to provide glasses having not only an index of refraction n_(e) which exceeds the index of 1.57 and an Abbe number ν_(e) lower than 70, but also having a relatively high positive anomalous partial dispersion +Δν_(e).

Another object of the present invention is to provide a process of producing such glasses with a high index of refraction, a low Abbe number, and a high positive anomalous partial dispersion.

Other objects of the present invention and advantageous features thereof will become apparent as the description proceeds.

In principle these objects are achieved in accordance with the present invention by producing glasses by melting a glass component mixture of the following components, in weight percent:

a.

0.1 % to 1.5 % of magnesium fluoride MgF₂,

0.1 % to 1.5 % of calcium fluoride CaF₂,

up to 15.0 % of strontium fluoride SrF₂,

up to 25.0 % of barium fluoride BaF₂,

up to 10.0 % of aluminum fluoride AlF₃, and

0.1 % to 1.5 % of lanthanum fluoride LaF₃,

the total amount of the alkaline earth metal fluorides to be used not exceeding about 38 % and the total amount of all the fluorides used not exceeding about 45 %;

b.

8.0 % to 12.0 % of aluminum metaphosphate Al(PO₃)₃,

3.0 % to 25.0 % of magnesium metaphosphate Mg(PO₃)₂,

10.0 % to 18.0 % of barium metaphosphate Ba(PO₃)₂,

the total amount of the metaphosphates used not exceeding about 50 %;

c.

8.0 % to 55.0 % of barium oxide BaO;

d.

up to 17.0 % of boron trioxide B₂ O₃,

up to 10.0 % of germanium dioxide GeO₂,

up to 4.0 % of titanium dioxide TiO₂, and

up to 20.0 % of niobium pentoxide Nb₂ O₅.

It is also possible to produce glasses according to the present invention by melting a mixture consisting of the following components, in weight percent:

a.

0.4 % to 0.5 % of magnesium fluoride MgF₂,

0.5 % to 0.6 % of calcium fluoride CaF₂,

up to 13.0 % of strontium fluoride SrF₂,

up to 22.0 % of barium fluoride BaF₂,

up to 8.0 % of aluminum fluoride AlF₃, and

0.5 % to 0.6 % of lanthanum fluoride LaF₃,

the total amount of the alkaline earth metal fluorides to be used not exceeding about 35 % and the total amount of all the fluorides used not exceeding about 43 %;

b.

9.0 % to 10.0 % of aluminum metaphosphate Al(PO₃)₃,

4.0 % to 23.0 % of magnesium metaphosphate Mg(PO₃)₂,

11.0 % to 15.0 % of barium metaphosphate Ba(PO₃)₂,

the total amount of the metaphosphates used not exceeding about 47 %;

c.

10.0 % to 52.0 % of barium oxide BaO;

d.

up to 15.0 % boron trioxide B₂ O₃,

up to 8.0 % of germamium dioxide GeO₂,

up to 2.0 % of titanium dioxide TiO₂, and

up to 18.0 % of niobium pentoxide Nb₂ O₅.

According to a preferred embodiment of the present invention the mixture of glass components to yield a glass of the present invention may consist of the following agents, in weight percent:

a.

0.44 % of magnesium fluoride MgF₂,

0.53 % of calcium fluoride CaF₂,

up to 12.2 % of strontium fluoride SrF₂,

up to 21.5 % of barium fluoride BaF₂,

up to 7.5 % of aluminum fluoride AlF₃,

0.53 % of lanthanum fluoride LaF₃,

the total amount of the alkaline earth metal fluorides used not being less than 0.97 % and not exceeding 34.67 %, and the total amount of all the fluorides used not being less than 1.5 % and not exceeding 42.7 %;

b.

9.3 % of aluminum metaphosphate Al(PO₃)₃,

4.5 % to 22.5 % of magnesium metaphosphate Mg(PO₃)₂,

11.8 % to 14.8 % of barium metaphosphate Ba(PO₃)₂,

the total amount of the metaphosphates used not being less than 28.6 % and not exceeding 46.6 %;

c.

10.7 % to 51.9 % of barium oxide BaO;

d.

up to 15.0 % of boron trioxide B₂ O₃,

up to 7.5 % of germanium dioxide GeO₂,

up to 1.5 % of titanium dioxide TiO₂, and

up to 18.0 % of niobium pentoxide Nb₂ O₅.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, the particular optical parameters of glasses produced according to the present invention are shown. In said drawings:

FIG. 1 shows the optical position range of the glasses produced by the process of the present invention in an n_(e) -ν_(e) diagram as compared with known glasses, and

FIG. 2 shows the optical position range of the glasses produced by the process of the present invention in a θ'_(g) -ν_(e) diagram.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fluorophosphate glasses according to the present invention are produced, for instance, by melting mixtures composed as listed in the following Table but not limited to the amounts of components as given therein. The amounts given in the Table are amounts in weight percent.

    Melt No.:                                                                            1   2    3    4    5    6    7    8    9                                 __________________________________________________________________________     Mg(PO.sub.3).sub.2                                                                   22.50                                                                              22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                             Ba(PO.sub.3).sub.2                                                                   14.80                                                                              14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                             Al(PO.sub.3).sub.3                                                                   9.30                                                                               9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30                              MgF.sub.2                                                                            0.44                                                                               0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44                              CaF.sub.2                                                                            0.53                                                                               0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53                              SrF.sub.2                                                                            12.20                                                                              12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               9.20                              BaF.sub.2                                                                            21.50                                                                              18.50                                                                               15.50                                                                               12.50                                                                               9.50 6.50 3.50 --   --                                AlF.sub.3                                                                            7.50                                                                               7.50 7.50 7.50 7.50 7.50 7.50 7.50 7.50                              LaF.sub.3                                                                            0.53                                                                               0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53                              BaO   10.70                                                                              13.70                                                                               16.70                                                                               19.70                                                                               22.70                                                                               25.70                                                                               28.70                                                                               32.20                                                                               35.20                             B.sub.2 O.sub.3                                                                      --  --   --   --   --   --   --   --   --                                GeO.sub.2                                                                            --  --   --   --   --   --   --   --   --                                TiO.sub.2                                                                            --  --   --   --   --   --   --   --   --                                Nb.sub.2 O.sub.5                                                                     --  --   --   --   --   --   --   --   --                                __________________________________________________________________________     n.sub.e                                                                              1.5753                                                                             1.5763                                                                              1.5766                                                                              1.5781                                                                              1.5801                                                                              1.5820                                                                              1.5845                                                                              1.5878                                                                              1.5928                            ν.sub.e                                                                           69.6                                                                               69.6 69.7 69.5 68.8 68.7 68.8 68.4 67.6                              Δν.sub.e                                                                    +10.9                                                                              +10.4                                                                               +10.6                                                                               +9.3 +6.6 +8.2 +8.1 +9.0 +7.0                              θ'.sub.g                                                                       0.4836                                                                             0.4828                                                                              0.4833                                                                              0.4814                                                                              0.4786                                                                              0.4808                                                                              0.4808                                                                              0.4825                                                                              0.4809                            __________________________________________________________________________     Melt No.:                                                                            10  11   12   13   14   15   16   17   18   15a                          __________________________________________________________________________     Mg(PO.sub.3).sub.2                                                                   22.50                                                                              22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                                                                               22.50                        Ba(PO.sub.3).sub.2                                                                   14.80                                                                              14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                        Al(PO.sub.3).sub.3                                                                   9.30                                                                               9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30                         MgF.sub.2                                                                            0.44                                                                               0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44                         CaF.sub.2                                                                            0.53                                                                               0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53                              SrF.sub.2                                                                            6.20                                                                               3.20 --   --   --   --   12.20                                                                               12.20                                                                               12.20                                                                               --                           BaF.sub.2                                                                            --  --   --   --   --   --   --   --   --   --                           AlF.sub.3                                                                            7.50                                                                               7.50 7.50 4.50 2.00 --   7.50 7.50 7.50 1.00                         LaF.sub.3                                                                            0.53                                                                               0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53                         BaO   38.20                                                                              41.20                                                                               44.40                                                                               47.40                                                                               49.90                                                                               51.90                                                                               31.70                                                                               31.20                                                                               30.70                                                                               50.90                        B.sub.2 O.sub.3                                                                      --  --   --   --   --   --   --   --   --   --                           GeO.sub.2                                                                            --  --   --   --   --   --   --   --   --   --                           TiO.sub.2                                                                            --  --   --   --   --   --   0.50 1.00 1.50 --                           Nb.sub.2 O.sub.5                                                                     --  --   --   --   --   --   --   --   --   --                           __________________________________________________________________________     n.sub.e                                                                              1.5963                                                                             1.6012                                                                              1.6073                                                                              1.6175                                                                              1.6267                                                                              --   1.5926                                                                              1.5931                                                                              1.5986                                                                              1.6107                       ν.sub.e                                                                           67.2                                                                               66.4 65.7 64.3 62.7 --   65.7 63.7 61.4 64.65                        Δν.sub.e                                                                    +6.9                                                                               +7.5 +5.5 +6.1 +5.6 --   + 9.1                                                                               +8.7 +8.3 +9.5                         θ'.sub.g                                                                       0.4813                                                                             0.4833                                                                              0.4815                                                                              0.4843                                                                              0.4859                                                                              --   0.4866                                                                              0.4888                                                                              0.4916                                                                              0.4887                       __________________________________________________________________________     Melt No.:                                                                            19  20   21   22   23   24   25   26   27                                __________________________________________________________________________     Mg(PO.sub.3).sub.2                                                                   22.50                                                                              22.50                                                                               22.50                                                                               22.50                                                                               19.50                                                                               16.50                                                                               13.50                                                                               10.50                                                                               7.50                              Ba(PO.sub.3).sub.2                                                                   14.80                                                                              14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                             Al(PO.sub.3).sub.2                                                                   9.30                                                                               9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30                              MgF.sub.2                                                                            0.44                                                                               0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44                              CaF.sub.2                                                                            0.53                                                                               0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53                         SrF.sub.2                                                                            12.20                                                                              12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                             BaF.sub.2                                                                            --  --   --   --   --   --   --   --   --                                AlF.sub.3                                                                            7.50                                                                               7.50 7.50 7.50 7.50 7.50 7.50 7.50 7.50                              LaF.sub.3                                                                            0.53                                                                               0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53                              BaO   29.20                                                                              26.20                                                                               27.70                                                                               29.20                                                                               32.20                                                                               32.20                                                                               32.20                                                                               32.20                                                                               32.20                             B.sub.2 O.sub.3                                                                      --  --   --   --   --   --   --   --   --                                GeO.sub. 2                                                                           3.00                                                                               6.00 4.50 --   --   --   --   --   --                                TiO.sub.2                                                                            --  --   --   --   --   --   --   --   --                                Nb.sub.2 O.sub.5                                                                     --  --   --   3.00 3.00 6.00 9.00 12.00                                                                               15.00                             __________________________________________________________________________     n.sub.e                                                                              1.5915                                                                             1.5934                                                                              1.5922                                                                              1.5974                                                                              1.6005                                                                              1.6130                                                                              1.6285                                                                              1.6473                                                                              1.6676                            ν.sub.e                                                                           67.7                                                                               67.1 67.2 62.7 62.2 57.5 53.0 48.8 45.0                              Δν.sub.e                                                                    +9.5                                                                               +10.2                                                                               +6.5 +5.1 +6.2 +5.6 +4.8 +6.3 +6.5                              θ'.sub.g                                                                       0.4843                                                                             0.4862                                                                              0.4807                                                                              0.4852                                                                              0.4874                                                                              0.4932                                                                              0.4999                                                                              0.5066                                                                              0.5123                            __________________________________________________________________________     Melt No.:                                                                            28  29   30   31   32   33   34   35   34a  35a                          __________________________________________________________________________     Mg(PO.sub.3).sub.2                                                                   4.50                                                                               7.50 19.50                                                                               19.50                                                                               16.50                                                                               13.50                                                                               10.50                                                                               7.50 13.50                                                                               13.50                        Ba(PO.sub.3).sub.2                                                                   14.80                                                                              11.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                                                                               14.80                        Al(PO.sub.3).sub.2                                                                   9.30                                                                               9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30 9.30                         MgF.sub.2                                                                            0.44                                                                               0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44 0.44                         CaF.sub.2                                                                            0.53                                                                               0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53                         SrF.sub.2                                                                            12.20                                                                              12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               12.20                                                                               9.20 6.20                         BaF.sub.2                                                                            --  --   --   --   --   --   --   --   --   --                           AlF.sub.3                                                                            7.50                                                                               7.50 7.50 7.50 7.50 7.50 7.50 7.50 7.50 7.50                         LaF.sub.3                                                                            0.53                                                                               0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53 0.53                         BaO   32.20                                                                              32.20                                                                               27.70                                                                               32.20                                                                               32.20                                                                               32.20                                                                               32.20                                                                               32.20                                                                               32.20                                                                               32.20                        B.sub.2 O.sub.3                                                                      --  --   --   3.00 6.00 9.00 12.00                                                                               15.00                                                                               12.00                                                                               15.00                        GeO.sub.2                                                                            --  --   7.50 --   --   --   --   --   --   --                           TiO.sub.2                                                                            --  --   --   --   --   --   --   --   --   --                           Nb.sub.2 O.sub.5                                                                     18.00                                                                              18.00                                                                               --   --   --   --   --   --   --   --                           __________________________________________________________________________     n.sub.e                                                                              1.6910                                                                             1.6915                                                                              1.5949                                                                              1.6031                                                                              1.6049                                                                              1.6055                                                                              --   --   1.6077                                                                              1.6056                                                                              41.5.41.2.65.8 66.2                                                            766.4 65.9 -- -- 64                                                            .08 64.52               Δν.sub.e                                                                    +5.2                                                                               +6.4 +5.5 +6.6 + 8.9                                                                               +5.0 --   --   +4.5 +3.5                         θ'.sub.g                                                                       0.5155                                                                             0.5175                                                                              0.4812                                                                              0.4823                                                                              0.4881                                                                              0.4803                                                                              --   --   0.4823                                                                              0.4801                       __________________________________________________________________________

As shown by the examples given in the Table, glasses having high refraction values n_(e) > 1.57 and Abbe numbers ν_(e) between 70 and 41 are obtained. Such glasses retain surprisingly relatively high positive anomalous partial dispersion values +Δν_(e) due to providing, in addition to metaphosphates, also fluorides of bivalent or trivalent metals and oxides of bivalent to pentavalent elements as components of the mixtures in the ranges indicated and claimed hereinafter.

The graph illustrated in FIG. 1 shows the index of refraction n_(e) plotted on the ordinate and the Abbe number ν_(e) plotted on the abscissa. In said graph the glasses according to the present invention are indicated by a small solid triangle. Compared therewith the glasses of U.S. Pat. No. 3,492,136 are marked by a solid circle and the glasses of U.S. Pat. No. 3,671,276 are marked by a hollow circle. It is evident that all the examples of glasses according to this invention lie outside those regions of the n_(e) -ν_(e) field which are covered by the glasses disclosed in said two U.S. patents. The glasses of the present invention show, without any exception, higher n_(e) values and in general also lower Abbe numbers.

In the two-dimensional graphical showing of FIG. 1 the third important optical parameter of the fluorophosphate glasses, namely the positive anomalous partial dispersion value +Δν_(e), can, of course, not be taken into consideration. Said value becomes evident from FIG. 2. In the graph of said FIG. 2 the θ'_(g) value is plotted as ordinate and the Abbe number ν_(e) again as abscissa.

The following mathematical relationship applies to the two values θ'_(g) and ν_(e) : ##EQU1##

In said equations the subscripts e, g, F', and C' stand for concrete standard wavelengths.

The symbols used in FIG. 2 correspond to those used in FIG. 1. It is evident that all the glasses of the present invention lie to the right of the so-called "standard straight line". They, therefore, all have a positive Δν_(e), i.e. a +Δν_(e) glass has a higher ν_(e) value than a "standard" glass.

The following example serves to illustrate the manner in which the glass according to the present invention is produced by melting down a mixture of its components.

EXAMPLE

A well mixed charge, in weight percent, of the following composition is provided:

           Mg(PO.sub.3).sub.2                                                                       22.50 %                                                              Ba(PO.sub.3).sub.2                                                                       14.80 %                                                              Al(PO.sub.3).sub.3                                                                       9.30 %                                                               MgF.sub.2 0.44 %                                                               CaF.sub.2 0.53 %                                                               SrF.sub.2 12.20 %                                                              AlF.sub.3 7.50 %                                                               LaF.sub.3 0.53 %                                                               BaO       32.20 %                                                  

The mixture is melted in amounts of 2.5 kg. in a platinum crucible at 1000° C. Thereafter, the melting temperature is increased by about 100° C. to 1100° C. The melt is refined and homogenized at said temperature for 10 to 15 minutes. Thereupon, it is allowed to cool to 800° C. by discontinuing heat supply, while stirring, and is then poured into aluminum molds preheated to 530° C. The temperatures of melting, refining and homogenizing, cooling, and casting the glass component mixture may vary by ±5 %.

It is to be pointed out that additives customarily added in glass technology to the batches of glass component mixtures, for instance, additives for refining of the melt, such as alkali metal meta-arsenates, arsenates, bifluorides, and others in amounts not exceeding about 3 %, by weight, can be added to the glass component mixture without exceeding or substantially varying the scope of the present invention. Mixtures containing such additives which are within the scope of the attached claims thus are also comprised by them.

The temperature-time program as given hereinabove for carrying out the melting procedure represents also merely an example. The melting process can, of course, be modified by a person skilled in the art, depending on the specific charges of glass components employed.

The glasses according to the present invention are especially useful in apochromatically corrected objectives for microscopes and photographic apparatus, especially in telephoto lens systems.

It may be pointed out that the spectral wavelengths or spectral lines e, g, F', and C' of the equations given hereinabove are, respectively, the following lines:

e = green mercury line of the wavelength of 546.07 nm.

g = blue mercury line of the wavelength of 435.84 nm.

F' = blue cadmium line of the wavelength of 479.99 nm.

C' = red cadmium line of the wavelength of 643.85 nm. 

We claim:
 1. In a process of producing a fluorophosphate glass having an index of refraction n_(e) within the range of from about 1.5753 to about 1.6915, an Abbe number ν_(e) within the range of from about 41.2 to 69.7, and a relatively high positive anomalous partial dispersion, comprising the steps ofa. melting a mixture essentially consisting of the following components, in weight percent: Fluoride component (a)0.1% to 1.5% of magnesium fluoride MgF₂, 0.1% to 1.5% of calcium fluoride CaF₂, 0% to 15.0% of strontium fluoride SrF₂, 0% to 25.0% of barium fluoride BaF₂, 0% to 10.0% of aluminum fluoride AlF₃, and 0.1% to 1.5% of lanthanum fluoride LaF₃, the total sum of the alkaline earth metal fluorides in said mixture not exceeding 38% and the total sum of all fluorides in said mixture not exceeding 45%. Metaphosphate component (b)8.0% to 12.0% of aluminum metaphosphate Al(PO₃)₂, 3.0% to 25.0% of magnesium metaphosphate Mg(PO₃)₂, and 10.0% to 18.0% of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture not exceeding 50%; Barium oxide component (c)
 8. 0% to 55.0% of barium oxide BaO;Additional oxide component (d)0% to 17.0% of boron trioxide B₂ O₃, 0% to 10.0% of germanium dioxide GeO₂, 0% to 4.0% of titanium dioxide TiO₂, and 0% to 20.0% of niobium pentoxide Nb₂ O₅ ; b. homogenizing the molten mixture at a temperature within the range of from about 1000°C. to about 1100°C. with stirring; c. cooling said molten mixture to about 800°C.; and, d. pouring said mixture into preheated molds.
 2. The process of claim 1, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.4 % to 0.5 % of magnesium fluoride MgF₂, 0.5 % to 0.6 % of calcium fluoride CaF₂, 0 % to 13.0 % of strontium fluoride SrF₂, 0 % to 22.0 % of barium fluoride BaF₂, 0 % to 8.0 % of aluminum fluoride AlF₃, and 0.5 % to 0.6 % of lanthanum fluoride LaF₃ ; the total sum of the alkaline earth metal fluorides in said mixture not exceeding the sum of 35 % and the total sum of all fluorides not exceeding 43 %; Metaphosphate component (b)9.0 % to 10.0 % of aluminum metaphosphate Al(PO₃)₃, 4.0 % to 23.0 % of magnesium metaphosphate Mg(PO₃)₂, and 11.0 % to 15.0 % of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture not exceeding 47 %; Barium oxide component (c)10.0 % to 52.0 % of barium oxide BaO; and Additional oxide component (d)0 % to 15.0 % of boron trioxide B₂ O₃, 0 % to 8.0 % of germanium dioxide GeO₂, 0 % to 2.0 % of titanium dioxide TiO₂, and 0 % to 18.0 % of niobium pentoxide Nb₂ O₅.
 3. The process of claim 1 in which the mixture consists of the following components, in weight percent:Fluoride component (a)
 0. 44 % of magnesium fluoride MgF₂,0.53 % of calcium fluoride CaF₂, 0 % to 12.2 % of strontium fluoride SrF₂, 0 % to 21.5 % of barium fluoride BaF₂, 0 % to 7.5 % of aluminum fluoride AlF₃, and 0.53 % of lanthanum fluoride LaF₃, the total sum of the alkaline earth metal fluorides being at least 0.97 % and not exceeding 34.67 % and the total sum of all fluorides in said mixture being at least 1.5 % and not exceeding 42.7 %; Metaphosphate component (b)9.3 % of aluminum metaphosphate Al(PO₃)₃, 4.5 % to 22.5 % of magnesium metaphosphate Mg(PO₃)₂, and 11.8 % to 14.8 % of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture being at least 28.6 % and not exceeding 46.6 %; Barium oxide component (c)10.7 % to 51.9 % of barium oxide BaO; and Additional oxide component (d)0 % to 15.0 % of boron trioxide B₂ O₃, 0 % to 7.5 % of germanium dioxide GeO₂, 0 % to 1.5 % of titanium dioxide TiO₂, and 0 % to 18.0 % of niobium pentoxide Nb₂ O₅.
 4. A batch composition for making fluorophosphate glass having an index of refraction n_(e) within the range of from about 1.5753 to about 1.6915, an Abbe number ν_(e) within the range of from about 41.2 to 69.7, and a relatively high positive anomalous partial dispersion, said composition essentially consisting of the following components, in weight percent:Fluoride component (a)0.1% to 1.5% of magnesium fluoride MgF₂, 0.1% to 1.5% of calcium fluoride CaF₂, 0% to 15.0% of strontium fluoride SrF₂, 0% to 25.0% of barium fluoride BaF₂, 0% to 10.0% of aluminum fluoride AlF₃, and 0.1% to 1.5% of lanthanum fluoride LaF₃, the total sum of the alkaline earth metal fluorides in said mixture not exceeding 38% and the total sum of all fluorides in said mixture not exceeding 45%; Metaphosphate component (b)8.0% to 12% of aluminum metaphosphate Al(PO₃)₂, 3.0% to 25.0% of magnesium metaphosphate Mg(PO₃)₂, and 10.0% to 18.0% of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture not exceeding 50%; Barium oxide component (c)8.0% to 55.0% of barium oxide BaO; Additional oxide component (d)0% to 17.0% of boron trioxide B₂ O₃, 0% to 10.0% of germanium dioxide GeO₂, 0% to 4.0% of titanium dioxide TiO₂, and 0% to 20.0% of niobium pentoxide Nb₂ O₅.
 5. The composition of claim 4, in which the mixture consists of the following components, in weight percent:Fluoride component (a)
 0. 4 % to 0.5 % of magnesium fluoride MgF₂,0.5 % to 0.6 % of calcium fluoride CaF₂, 0 % to 13.0 % of strontium fluoride SrF₂, 0 % to 22.0 % of barium fluoride BaF₂, 0 % to 8.0 % of aluminum fluoride AlF₃, and 0.5 % to 0.6 % of lanthanum fluoride LaF₃ ; the total sum of the alkaline earth metal fluorides in said mixture not exceeding the sum of 35 % and the total sum of all fluorides not exceeding 43 %; Metaphosphate component (b)9.0 % to 10.0 % of aluminum metaphosphate Al(PO₃)₃, 4.0 % to 23.0 % of magnesium metaphosphate Mg(PO₃)₂, and 11.0 % to 15.0 % of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture not exceeding 47 %; Barium oxide component (c)10.0 % to 52.0 % of barium oxide BaO; and Additional oxide component (d)0 % to 15.0 % of boron trioxide B₂ O₃, 0 % to 8.0 % of germanium dioxide GeO₂, 0 % to 2.0 % of titanium dioxide TiO₂, and 0 % to 18.0 % of niobium pentoxide Nb₂ O₅.
 6. The composition of claim 4, in which the mixture consists of the following components, in weight percent:Fluoride component (a)
 0. 44 % of magnesium fluoride MgF₂,0.53 % of calcium fluoride CaF₂, 0 % to 12.2 % of strontium fluoride SrF₂, 0 % to 21.5 % of barium fluoride BaF₂, 0 % to 7.5 % of aluminum fluoride AlF₃, and 0.53 % of lanthanum fluoride LaF₃, the total sum of the alkaline earth metal fluorides being at least 0.97 % and not exceeding 34.67 % and the total sum of all fluorides in said mixture being at least 1.5 % and not exceeding 42.7 %; Metaphosphate component (b)9.3 % of aluminum metaphosphate Al(PO₃)₃, 4.5 % to 22.5 % of magnesium metaphosphate Mg(PO₃)₂, and 11.8 % to 14.8 % of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture being at least 28.6 % and not exceeding 46.6 %; Barium oxide component (c)10.7 % to 51.9 % of barium oxide BaO; and Additional oxide component (d)0 % to 15.0 % of boron trioxide B₂ O₃, 0 % to 7.5 % of germanium dioxide GeO₂, 0 % to 1.5 % of titanium dioxide TiO₂, and 0 % to 18.0 % of niobium pentoxide Nb₂ O₅.
 7. The composition of claim 4, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.44 % of magnesium fluoride MgF₂, 0.53 % of calcium fluoride CaF₂, 12.20 % of strontium fluoride SrF₂, 7.50 % of aluminum fluoride AlF₃, and 0.53 % of lanthanum fluoride LaF₃ ; Metaphosphate component (b)9.30 % of aluminum metaphosphate Al(PO₃)₃, 22.50 % of magnesium metaphosphate Mg(PO₃)₂, and 14.80 % of barium metaphosphate Ba(PO₃)₂ ; and Barium oxide component (c)32.20 % of barium oxide BaO.
 8. The composition of claim 4, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.44 % of magnesium fluoride MgF₂, 0.53 % of calcium fluoride CaF₂, 12.20 % of strontium fluoride SrF₂, 7.50 % of aluminum fluoride AlF₃, and 0.53 % of lanthanum fluoride LaF₃ ; Metaphosphate component (b)9.30 % of aluminum metaphosphate Al(PO₃)₃, 22.50 % of magnesium metaphosphate Mg(PO₃)₂, and 14.80 % of barium metaphosphate Ba(PO.sub. 3)₂ ; Barium oxide component (c)29.20 % of barium oxide BaO; and Additional oxide component (d)3.00 % of germanium oxide GeO₂.
 9. A fluorophosphate glass having an index of refraction n_(e) within the range of from about 1.5753 to about 1.6267, an Abbe number ν_(e) within the range of from about 61.4 to about 69.7, and a relatively high positive anomalous partial dispersion, said glass being produced by melting a mixture essentially consisting of the following components, in weight percent:Fluoride component (a)0.1% to 1.5% of magnesium fluoride MgF₂, 0.1% to 1.5% of calcium fluoride CaF₂, 0% to 15.0% of strontium fluoride SrF₂, 0% to 25.0% of barium fluoride BaF₂, 0% to 10.0% of aluminum fluoride AlF₃, and 0.1% to 1.5% of lanthanum fluoride LaF₃, the total sum of the alkaline earth metal fluorides in said mixture not exceeding 38% and the total sum of all fluorides in said mixture not exceeding 45%; Metaphosphate component (b)8.0% to 12% of aluminum metaphosphate Al(PO₃)₂, 3.0% to 25.0% of magnesium metaphosphate Mg(PO₃)₂, and 10.0% to 18.0% of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture not exceeding 50%; Barium oxide component (c)
 8. 0% to 55.0% of barium oxide BaO;Additional oxide component (d)0% to 17.0% of boron trioxide B₂ O₃, 0% to 10.0% of germanium dioxide GeO₂, and 0% to 4.0% of titanium dioxide TiO₂.
 10. The fluorophosphate glass of claim 9, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.4% to 0.5% of magnesium fluoride MgF₂, 0.5% to 0.6% of calcium fluoride CaF₂, 0% to 13.0% of strontium fluoride SrF₂, 0% to 22.0% of barium fluoride BaF₂, 0% to 8.0% of aluminum fluoride AlF.sub. 3, and 0.5% to 0.6% of lanthanum fluoride LaF₃ ; the total sum of the alkaline earth metal fluorides in said mixture not exceeding the sum of 35% and the total sum of all fluorides not exceeding 43%; Metaphosphate component (b)9.0% to 10.0% of aluminum metaphosphate Al(PO₃)₃, 4.0% to 23.0% of magnesium metaphosphate Mg(PO₃)₂, and 11.0% to 15.0% of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture not exceeding 47%; Barium oxide component (c)
 10. 0% to 52.0% of barium oxide BaO; andAdditional oxide component (d)0% of boron trioxide B₂ O₃, 0% to 8.0% of germanium dioxide GeO₂, 0% to 2.0% of titanium dioxide TiO₂,
 11. The fluorophosphate glass of claim 9, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.44% of magnesium fluoride MgF₂, 0.53% of calcium fluoride CaF₂, 0% to 12.2% of strontium fluoride SrF₂, 0% to 21.5% of barium fluoride BaF₂, 0% to 7.5% of aluminum fluoride AlF₃, and 0.53% of lanthanum fluoride LaF₃, the total sum of the alkaline earth metal fluorides being at least 0.97% and not exceeding 34.67% and the total sum of all fluorides in said mixture being at least 1.5% and not exceeding 42.7%; Metaphosphate component (b)9.3% of aluminum metaphosphate Al(PO₃)₃, 4.5% to 22.5% of magnesium metaphosphate Mg(PO₃)₂, and 11.8% to 14.8% of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture being at least 28.6% and not exceeding 46.6%; Barium oxide component (c)
 10. 7% to 51.9% of barium oxide BaO; andAdditional oxide component (d):0% to 15.0% of boron trioxide B₂ O₃, 0% to 7.5% of germanium dioxide GeO₂, 0% to 1.5% of titanium dioxide TiO₂.
 12. The fluorophosphate glass of claim 9, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.44% of magnesium fluoride MgF₂, 0.53% of calcium fluoride CaF₂, 12.20% of strontium fluoride SrF₂, 7.50% of aluminum fluoride AlF₃, and 0.53% of lanthanum fluoride LaF₃ ; Metaphosphate component (b)9.30% of aluminum metaphosphate Al(PO₃)₃, 22.50% of magnesium metaphosphate Mg(PO₃)₂, and 14.80% of barium metaphosphate Ba(PO₃)₂ ; and Barium oxide component (c)32.20% of barium oxide BaO.
 13. The fluorophosphate glass of claim 9, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.44% of magnesium fluoride MgF₂, 0.53% of calcium fluoride CaF₂, 12.20% of strontium fluoride SrF₂, 7.50% of aluminum fluoride AlF₃, and 0.53% of lanthanum fluoride LaF₃ ; Metaphosphate component (b)9.30% of aluminum metaphosphate Al(PO₃)₃, 22.50% of magnesium metaphosphate Mg(PO₃)₂, and 14.80% of barium metaphosphate Ba(PO₃)₂ ; Barium oxide component (c)29.20% of barium oxide BaO; and Additional oxide component (d)3.00% of germanium oxide GeO₂.
 14. A fluorophosphate glass having an index of refraction n_(e), within the range of from about 1.5974 to 1.6915, an Abbe number ν_(e) within the range of from about 41.2 to 62.7 and a relatively high positive anomalous partial dispersion, said glass being produced by melting a mixture essentially consisting of the following components, in weight percent:Fluoride component (a)
 0. 1% to 1.5% of magnesium fluoride MgF₂,0.1% to 1.5% of calcium fluoride CaF₂, 0% to 15.0% of strontium fluoride SrF₂, 0% to 25.0% of barium fluoride BaF₂, 0% to 10.0% of aluminum fluoride AlF₃, and 0.1% to 1.5% of lanthanum fluoride LaF₃, the total sum of the alkaline earth metal fluorides in said mixture not exceeding 38% and the total sum of all fluorides in said mixture not exceeding 45%; Metaphosphate component (b)8.0% to 12% of aluminum metaphosphate Al(PO₃)₂, 3.0% to 25.0% of magnesium metaphosphate Mg(PO₃)₂, and 10.0% to 18.0% of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture not exceeding 50%; Barium oxide component (c)8.0% to 55.0% of barium oxide BaO; Additional oxide component (d)0% to 17.0% of boron trioxide B₂ O₃, 0% to 10.0% of germanium dioxide GeO₂, 0% to 4.0% of titanium dioxide TiO₂, and 3.0% to 18.0% of niobium pentoxide Nb₂ O₅.
 15. The fluorophosphate glass of claim 14, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.44% of magnesium fluoride MgF₂, 0.53% of calcium fluoride CaF₂, 0% to 12.2% of strontium fluoride SrF₂, 0% to 21.5% of barium fluoride BaF₂, 0% to 7.5% of aluminum fluoride AlF₃, and 0.53% of lanthanum fluoride LaF₃, the total sum of the alkaline earth metal fluorides being at least 0.97% and not exceeding 34.67% and the total sum of all fluorides in said mixture being at least 1.5% and not exceeding 42.7%; Metaphosphate component (b)9.3% of aluminum metaphosphate Al(PO₃)₃, 4.5% to 22.5% of magnesium metaphosphate Mg(PO₃)₂, and 11.8% to 14.8% of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture being at least 28.6% and not exceeding 46.6%; Barium oxide component (c)32.2% of barium oxide BaO; and Additional oxide component (d)0% to 15.0% of boron trioxide B₂ O₃, 0% to 15.0% of boron trioxide B₂ O₃, 0% to 7.5% of germanium dioxide GeO₂, 0% to 1.5% of titanium dioxide TiO₂, and 3.0% to 18.0% of niobium pentoxide Nb₂ O₅.
 16. The fluorophosphate glass of claim 15, in which the mixture consists of the following components, in weight percent:Fluoride component (a)0.44% of magnesium fluoride MgF₂, 0.53% of calcium fluoride CaF₂, 12.20% of strontium fluoride SrF₂, 7.5% of aluminum fluoride AlF₃, and 0.53% of lanthanum fluoride LaF₃ ; Metaphosphate component (b)9.3% of aluminum metaphosphate Al(PO₃)₃, 4.5% to 22.5% of magnesium metaphosphate Mg(PO₃)₂, and 11.8% to 14.8% of barium metaphosphate Ba(PO₃)₂, the total sum of the metaphosphates in said mixture being at least 28.6% and not exceeding 46.60%; Barium oxide component (c)32.2% of barium oxide BaO; and Additional oxide component (d)3.0% to 18.0% of niobium pentoxide Nb₂ O₅. 